The invention relates to stress reduction in the interface between a blade dovetail and a wheel slot and, more particularly, to a dovetail section including an undercut fillet radius having a multi-part profile shape formed at an intersection of the dovetail platform and a dovetail pressure surface.
FIGS. 1 and 2 show a conventional compressor blade assembly including a blade 12 fixed to a dovetail section 14, which is attachable to a compressor wheel (not shown). An analysis of a failed blade shows that the failure resulted from fretting on the dovetail pressure surfaces 16 near the small fillet radius 18 that transitions from the blade neck 20 to the dovetail platform 22. The analysis showed the stress in the small 0.022 fillet radius 18 was substantial enough to grow micro-cracks in the fretted area eventually causing ultimate failure (blade liberation). A subsequent review of several hundred parts showed fretting was prevalent in these areas in nearly all parts observed.
An undercut radius concept on compressor blade dovetails has been previously proposed. See, for example, U.S. Pat. No. 6,769,877. A subsequent dovetail section design incorporated a “P-cut” feature 24 as shown in FIG. 2. The P-cut feature 24 in the dovetail 14 creates a change in the stress profile unlike that seen on a typical compressor blade dovetail. The prior undercut radius concept did not accommodate this unique stress profile and had a negative affect on the design stress parameters of the P-cut section 24.